Keep Your SD Cards Data Safe With The SD Locker

November 12, 2013 by 41 Comments

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[Karl Lunt] has come up with a simple circuit for protecting data you have stored on SD cards. As is relatively well-known, the little lock switch on the side of most SD cards really doesn’t do anything more than the switch on floppies or the tabs on VHS or cassette decks. It’s up to the reader/writer to check the status of the tab and decide if it should write to the card or not. Not a very safe system. However, it’s not the only write protection system built into SD and SDHC cards. As part of the standard, cards have three protection methods: A TMP_WRITE_PROTECT bit, a PERM_WRITE_PROTECT bit, and a PWD register.

The PERM_WRITE_PROTECT bit permanently write protects the card. The bit can not be reset, so you should be really sure you want to keep the data on the card forever. The PWD register is a password register. The card will not allow any access (read or write) unless a password is provided. The TMP_WRITE_PROTECT bit is a temporary write protect. This is the bit that [Karl] is working with. When TMP_WRITE_PROTECT is set, the card can be read but not written. Note that there is no true protection here, as anyone can modify the bit. However, this should stop grandma from accidentally deleting your wedding pictures.

[Karl’s] device is very simple. A card is inserted into an Altoids tin enclosure. One button locks the card, another unlocks it. Three LEDs return status – power, card locked, and card unlocked. Under the hood, he’s using an Atmel ATmega328 to set and clear the TMP_WRITE_PROTECT bits. Power is provided by two AA batteries, and regulated with a Pololu 3.3v boost regulator. [Karl] has also included a serial port for control and debug information. We think this is a great hack, however one thing we’re not sure of is how or if these features are implemented in all cards. We’re relatively sure the name brand cards stick to the SD/SDHC spec sheet, but what about all the knockoff and no name brands from overseas?

The Tiniest SD Card Locker

January 18, 2014 by 45 Comments

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In case you weren’t aware, that little ‘write protect’ switch on your SD cards probably doesn’t do anything. It’s only a switch, really, and if an SD card reader doesn’t bother to send that signal to your computer, it’s completely ineffective. Then there’s the question of your OS actually doing something with that write protect signal.

The better way to go about write protecting an SD card is using the TMP_WRITE_PROTECT bit on the SD card’s controller. [Nephiel] came up with an amazingly small device to set that bit, with the entire circuit fitting inside an old Playstation memory card.

[Nephiel] based his project on [Karl Lunt]’s SD Card Locker we saw late last year. [Karl]’s SD Locker uses an ATMega328 microcontroller, a pair of AA batteries, and an SD card socket to perform the bit toggling. This is still a very small device that fits inside an Altoids tin, but [Nephiel] thought he could make it smaller.

The new and improved version uses an ATTiny85 for SPI access to the SD card. A single button and LED serves as the user interface: with the LED off, the SD card is writable. Press the button, the card is locked, and the LED lights up.

Update: SD Card Locker Now Supports Password Protect

November 27, 2013 by 19 Comments

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[Karl Lunt] has updated his Secure Digital Card locker to support password based locking. [Karl’s] original design only supported write locking via the TMP_WRITE_PROTECT  bit. The new design gives the user an option: TMP_WRITE_PROTECT, or password protection. [Karl] goes into further detail this time around about the bit fields used with CMD42, and how they are set. The passwords in this case are up to 16 bytes. The bytes don’t necessarily have to be printable characters – any binary value can be used. Unfortunately, [Karl’s] locker doesn’t utilize a user interface beyond the buttons, so any password must be “baked in” to the SD Card locker firmware. We would love to see the option of even a basic serial interface for entering a password (most likely in hex).

[Karl] tried his device out with several different cards, and several computers. While not an exhaustive test, he did find that the computers always behaved the same: A locked SD card would not show up. In the case of windows, no beep, no drive, nothing. He goes into the security possibilities of using password locking: Financial data could be stored and physically transferred via SD or microSD, with the password sent separately (say in an email or SMS). Any unenlightened data thief attempting to use the card would think they have a broken device on their hands.

We don’t know how secure the password lock feature is – brute forcing a variable length 16 byte binary password would take some time. It all comes down to how quickly each password attempt takes. Some cursory web searching didn’t bring up any information about successful SD card password cracking. Sounds like a challenge for our readers!

T-Mobile SDA Unlocking, Overclocking And Skype

July 8, 2006 by 20 Comments

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[Ken Keiter] has written up a guide to unlocking your T-Mobile SDA, overclocking it, and then adding Skype for use over WiFi. The unlock procedure is pretty simple and only needs some free software. The overclocking is just as simple. The OMAP processor needs to be overclocked to 240MHz otherwise Skype will have a lot of lag. The Skype install is straightforward except for one hitch: the phone doesn’t have a touch screen so you can’t click Sign-In. You can get around this using a piece of software called Pocket Controller which lets you click the button with your mouse. After that you can set Skype to auto sign-in so you’ll never need to use the mouse again. Ken’s final tip is how to change the T-Zones button so that it launches Skype.

The Pi Pico, An SDR Receiver Front End

June 5, 2024 by 21 Comments

Making a software defined radio (SDR) receiver is a relatively straightforward process, given the right radio front end electronics and analogue-to-digital converters. Two separate data streams are generated using clocks at a 90 degree phase shift, and these are passed to the software signal processing for demodulation. But what happens if you lack a pair of radio front ends and a suitable clock generator? Along comes [Mordae] with an SDR using only the hardware on a Raspberry Pi Pico. The result is a fascinating piece of lateral thinking, extracting something from the hardware that it was never designed to do.

The onboard RP2040 ADC is of course far too slow for the task, so instead an input is used, with a negative feedback arrangement from another GPIO to form a crude 1-bit ADC. A PIO peripheral is then used to perform the quadrature mixing, resulting in the requisite pair of data streams. At this point these are sent over USB to GNU Radio for demodulating, mainly for convenience rather than necessarily because the microcontroller lacks the power.

The result is a working SDR front end, demonstrated pulling in an FM broadcast station. The Pico has to be overclocked to reach that frequency and it’s more than a little noisy, but we’re extremely impressed with how much has been done with so little. Oddly it isn’t the first Pico SDR we’ve seen, but the previous one was a much more conventional and lower-frequency affair for the European Long Wave band.

Breadboard SDR Doesn’t Need Much

March 19, 2024 by 10 Comments

[Grug Huhler] built a simple Tayloe mixer and detector on a breadboard. He decided to extend it a bit to be a full-blown software defined radio (SDR). He then used WSJT-X to monitor FT8 signals and found that he could pick up signals from all over the world with the little breadboard system.

A Raspberry Pi Pico generates a quadrature clock that acts as the local oscillator for the radio. All the processing of the input signal to a quadrature signal is done with a 74LV4052A, which is nothing more than an analog multiplexer. In principle, the device takes a binary number from zero to three and uses it to connect a common signal to one of four channels. There are two common lines and two sets of four channels. In this case, only half of the chip is in use.

An antenna network (two resistors and a capacitor) couples the antenna to one of the common pins, and the Pi generates two square waves, 90 degrees out of phase with each other. This produces select signals in binary of 00, 01, 11, and 10. An op amp and a handful of passive components couple the resulting signals to a PC soundcard, where the software processes the data. The Pi can create clocks up to about 15 or 20 MHz easily using the PIO.

The antenna is a 20-meter-long wire outside, and that accounts for some of the radio’s success. There are several programs than can work with soundcard input like this and [Grug] shows Quisk as a general-purpose receiver. If you missed the first video explaining the Tayloe mixer design, you can catch it below the first video.

This isn’t the first breadboard SDR we’ve seen, but they all use different parts. We’ve even seen a one-bit SDR with three components total (not including the microcontroller). Seriously.

Continue reading “Breadboard SDR Doesn’t Need Much” →

Wiring An SD Card To A Handspring PDA’s 68K Bus With Only Three SOT23s

January 13, 2024 by 13 Comments

In 1998 the founders of Palm had a bit of a falling out with the wildly successful PDA company’s new owners. They set up a new company called Handspring, which enabled them to make PDAs again in the way they preferred, This resulted in the Handspring Visor line of PDAs, which featured a big cartridge slot called the Springboard Expansion slot. Much like a Gameboy, you could put in a range of modules, ranging from games to cameras to memory expansion and more. Since these modules connect directly to the internal Motorola 68k-based microprocessor, you could make a module either to comply with this standard or if you’re like [Dmitry], you’d figure out a way to get an SPI device like an SD card to communicate and expand storage.

Editor note: Dmitry’s design isn’t the first SD/MMC interface for the Visor. Portable Innovation Technology’s SD MemPlug Module supported SD/MMC way back in 2002. However – MemPlug was a commercial product, while Dmitry’s work is open source.

Continue reading “Wiring An SD Card To A Handspring PDA’s 68K Bus With Only Three SOT23s” →